1. Field Of The Invention
Physiological pressure measurement is a classical technical problem to which no acceptable solutions have been found in spite of considerable effort. It is commonly known to use liquid-filled catheters for providing hydraulic communication between the signal source (the body fluid) and the pressure sensor, which converts the hydrostatic pressure signals into electrical output signals. However, the hydraulic transfer in the catheter has severe limitations as regards the bandwidth (typically about ten Hz) and because of artifacts due to acceleration of the mass of liquid contained in the catheter.
2. Description of the Prior Art
These problems can be solved by miniaturizing the pressure sensor so that it can be located immediately at the signal source. A plurality of technical solutions of this problem have been suggested, making use of inductive, piezoresistive, capacitive or fiber optical pressure sensor elements. Certain types have also become available on the market and are to a certain extent used in animal tests and urological examinations in which the measuring practice and the hygienic requirements are less severe than for use in the heart and vessel system.
The reason for the limited use of miniaturized pressure sensors is primarily their inferior reliability, in combination with the fact that they usually have not been sufficiently adapted for standard clinical routines as regards possibilities of sterilization, compatability with other equipment, etc.
It is an object of the present invention to solve the above mentioned and related problems. A salient feature of the device according to the invention is that the miniaturized sensor element at any time during an ongoing examination can be tested against an externally generated calibration pressure. This offers a considerably increased reliability of the system compared to the prior art solutions. The device according to the invention includes at least one valve function capable of shutting off the signal pressure and instead connecting the calibration pressure. The valve function should be remotely controlled since repeated insertion and withdrawal of the sensor element would discomfort the patient, increase the risks of contamination and infectious hazards and require an increased x-ray dosage and cause other undesired effects. In the present invention the critical valve function is achieved by mechanical means, which has proven to result in a safer and more reliable function than alternative solutions making use of hydraulic or electromechanical control. The use of an automatic or semi-automatic calibration function further reduces the requirements on linearity, temperature stability and long term stability on the sensor element, which consequently can be of simpler design and have smaller dimensions. The latter increases the usefulness considerably since a larger number of body vessels become available for examination. An example thereof are the coronary vessels, in which pressure measurements can provide adequate information about stenosis and coverings. This would improve the possibilities of diagnosing and treating patients being in the danger-zone of having a myocardial infarction.